The Flux/Source boundary condition can be used on exterior boundaries only. With this node, the boundary condition is enforced according to
where g,
q, and the load factor
l can be specified. Here the dependent variable
u on the right-hand side is evaluated on the inside (as seen from the domain where the PDE interface is defined). When the normal vector is used in expressions for curved boundaries, it is important that the mesh version of these vectors is used. The components of this vector are denoted
nxmesh,
nymesh, and
nzmesh, respectively.
In this section you can enter a load factor l (default: 1). It is multiplied with the flux term g to form a flux term
g l. The use of the load factor is optional (the default of 1 means that it then has no effect), and it can be used for performance reasons. The load factor can be a scalar value or a global expression. Performance benefits are obtained when the
g expression can be factorized into a constant term and a time-varying load factor. For the
Flux/Source boundary condition this leads to the extra requirement that any flux part needs to be formulated with the
q term. For constant load factors, performance benefits are still obtained when the
g expression is linear in the dependent variables as long as the expression is not time dependent in other ways.
